3/18/2013 Post-Fukushima Research in Japan Masashi HIRANO

3/18/2013
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Japan Nuclear Energy Safety Organization:
International Research
– Post-Fukushima Research
Analysis with MELCORE
and OSCAAR
Post-Fukushima Research in Japan
Presented by
Masashi HIRANO
Japan Nuclear Energy Safety Organization (JNES)
U.S. NRC Regulatory Information Conference,
Washington, March 2013
Major Contributors

JNES
̶ Harutaka Hoshi
̶ Akitoshi Hotta
̶ Hideharu Sugino
̶ Ryuji Kubota
̶ Masami Kato
̶ Norikazu Yamada

Japan Atomic Energy Agency (JAEA)
– Masashi Iijima
– Toshimitsu Homma
– Hideo Nakamura
Contents
1
2
Overview
̶ Current Status of Fukushima-Daiichi and Safety
Regulation
 Some Examples of Safety Research
̶ Tsunami Hazard Evaluation Methods
̶ Analysis of Fukushima-Daiichi Accident:
(1) SA Progression and Source Terms
(2) Environmental Consequence Analysis
̶ Scrubbing under CV Wet Venting
̶ Effective Cooling of Containment Vessel (CV)
̶ Seawater and Boric Acid Injection
̶ LOCA at Spent Fuel Pool (SFP)
̶ Evaluation Methods of Safety Culture
̶ Off-site Radiological Effect on Residents and Workers
 Summary

1
3/18/2013
Current Status of Fukushima Dai-ichi
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 Stable debris cooling has been maintained in Units 1 to 3.
 RPV bottom temperatures and gaseous phase temperatures inside RPVs
were approximately 30-50°C (Nov. 6, 2012). SFP
 Visual inspection was done inside
PCVs with image scope,
thermocouple and dosimeter:
Ground
water
Injection
 In Unit 2, max. radiation dose was
intrusion
water pump
app. 73 Sv/h and water level was app.
60 cm from the bottom (Jan. 19 and
May 26–27, 2012).
 In Unit 1, max. radiation dose was
 New development:
app. 11.1 Sv/h and water level was
 “Multi-nuclide removal facility” is being
app. 2.8 m from the bottom (Oct. 9implemented to further reduce the contents
13, 2012).
of many nuclides such as Rb, Sr and Co
except tritium in the accumulated water.
Unit 1
Unit 2
 “Groundwater bypass” is planned to
reduce the ground water intrusion.
60cm
Pump well
2.8m
Reactor Building
Turbine Building
Permeable layer
Low-permeable layer
ANRE/METI, presented at OECD/NEA CSNI Meeting, Paris, Dec. 2012.
4
Current Status of Safety Regulation
 Only 2 units (Ohi Units 3 and 4) are in operation (48 units in shutdown).
 Nuclear Regulation Authority (NRA) was established on Sep. 19, 2012:
 NRA is establishing the new safety standards not only for DBAs but also for
Beyond-DBAs (BDBAs) including sever accidents (SAs) by creating task teams.
 The new standards will be applied to all existing NPPs (backfitting) and shall be
established by July, 2013.
Draft standards cover:
Approaches in
foreign countries:
 Beyond design basis external events to be considered:
• FLEX concept in US
• Extreme natural phenomena beyond design basis
• Hardened safety
• Aircraft crash, terrorism, etc.
core, bunkered
 BDBAs to be considered:
system, etc. in EU
• Use of insights from PRA
– Accident sequences leading to core damage
– Phenomena that could lead to CV failure:
Hydrogen explosion, DCH, MCCI, etc.
 Approaches for SA measures
• Robustness against beyond design basis external events
• Use of permanently installed systems and mobile equipment
• Reliability and environmental resistance/durability
http://www.nsr.go.jp/
 New guides for design basis earthquake and tsunami
Development of
Tsunami Hazard Evaluation Methods
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 For 2011 Tohoku Earthquake, JNES developed a tsunami source model taking
into account the plate tectonics and well reproduced the observed tsunami
waveforms at NPP sites (inversion analysis).
 By generalizing the this source model, JNES is
developing a probabilistic tsunami hazard
evaluation method.
Generalization
submerging plate
Slips in sub-fault in JNES source
model (Inversion analysis)
Application:
• Tsunami PRA
• Methods for
assessment of
design basis
tsunami
Tsunami intensity
(Tsunami height, etc.)
2
3/18/2013
Analysis of Fukushima-Daiichi
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(1) SA Progression and Source Terms
 The accident progression has been analyzed
with MELCOR developed by U.S.NRC.
 The analysis has been improved taking into
account the recent information such as:
 leakages from RPV and CV due to overtemperature, and
 thermal stratification in S/P.
 Release timings of FPs are relatively in good
agreement with the monitoring data.
Example of analysis results with
MELCORE:
PCV leakage assumed
Potential Leak locations
Monitoring data
1st Vent (Unit 1)
RPV and CV pressure
transients at Unit 2
2nd Vent (Unit 1)
From Unit 2
Vent (Unit 3)
Heat removal from S/P
suppressed D/W pressure
MELCOR
MELCOR
PCV
leakage
(Unit 1)
Plant records
Unit 1
Unit 2
Unit 3
Thermal stratification of S/P (subcooled
water remained) suppressed D/W pressure
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Analysis of Fukushima-Diichi Accident
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(2) Environmental Consequence Analysis
 By using the source terms with MELCOR (slide 6), an environmental
consequence analysis was done in JAEA with OSCAAR developed there.
Major findings:
Unit 1
Unit 1
Unit22
Unit
Unit 3
Total
Total sum
Total
 The release from Unit 2 on March 15
had dominant contribution to the inland
contamination.
 The release from Units 1 and 3 mostly
spread to the ocean.
 Sum of the release well reproduced the
characteristics of the measured
contamination.
Cs-137
Concentration
measured by
MEXT
(Nov. 5, 2011)
(Bq/m2)
Experimental Study on
Scrubbing under CV Wet Venting
 In Fukushima accident, some peaks in the
monitoring data might have been caused by CV
venting. This implies that scrubbing in S/P
might have been ineffective in reducing the
release of radioactive materials.
 JNES has started a study on scrubbing under
saturated water conditions taking into
account flashing accompanied by venting.
 Large Scale Integral Test
Height 10 m
Dia.
2m
Vol. 30 m 3
Max. Press. > 1MPa
Max. Temp. > 200°C
Underlying physical processes of
saturated scrubbing
Steam, aerosol,
non-condensable
gas
Aerosol
Gas release
Entrainment
Major mechanisms of aerosol
removal from bubbles
Bubble
breakup
Brown
diffusion
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Separator
Separator
Counter
Aerosol
counter
Test
Test
section
Vessel
Inertial
collision Aerosol
Aerosol
Aerosol
Counter
counter
Depress
urizing
Valve
Aerosol
Concentration
Sampling
Condensation/
evaporation
Formation of
large bubbles
Gravity
settlement
Steam,
Steam
NonNoncondensable
condensable
gas
Gas
Heating
Heating
Steam
Aerosol
Concentration
Sampling
Valve for
depressurization
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3/18/2013
Research on Effective Cooling
of Containment Vessel
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 The mission of Nuclear Safety Research Center (NSRC) in JAEA is a technical
support of safety regulation.
 Large-scale CV simulator under designing
 NSRC works on clarification
Facility
 Effectiveness of cooling methods,
Concept
of phenomena involved
Thermal stratification up to about 770 K,
Aerosol behavior and scrubbing
in BDBAs including SAs
 Small-scale CV
and confirmation of
simulator under
Sparger for
construction
effectiveness of existing
external cooling
and new AM measures.
 Development of
• New test facilities on CV
behavior to start in 2013
(small-scale) and 2015 (largescale)
Internal and external CV
cooling, aerosol behavior, etc
• Detailed measurement both
inside & outside of CV
• Development of CFD
methods for detailed
phenomena clarification
• Validation and improvement
of SA analysis methods to be
used for confirmation of
measures
measurement
methods
Spray
 Height : about 10 m
 Dia.: about 2.5 m
Steam
Gas sampling
 Height : about 1.5 m
 Dia.: about 1.5 m
He, N2, etc.
External cooling
Experimental Study on
Seawater and Boric Acid Injection
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 JNES plans to conduct a study on seawater / boric acid injection to identify the
salt and boric acid crystallization/precipitation characteristics and it’s
influences on fuel/debris cooling such as flow blockage for further
improving AM measures.
Small scale test for influence on
Test for precipitation at core
debris cooling at lower plenum
Seawater/boric acid
solution tank
• Laboratory scale small test: 200mm×200mm
Channel Box
×500 thickness
• Debris and crusts are simulated by alumina
particles with various diameters.
Separator
Seawater/boric acid
solution Tank
Online sampling
needles
Downcomer
Spacer
Spray
Salt
precipitation
Heater Rod
Water pool
area
Simulated
debris and
crust
Spacer
Pre-heater
Heat
conduction
plate
Seawater/boric acid 5x5 mockup
bundle
boiling loop
Overflow
tank
Electric
heaters
Thermo-couples
Thermal-Hydraulic Tests on LOCA
at Spent Fuel Pool
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 Regarding BDBAs at SFP, the draft safety standards require that measures
shall be taken to mitigate the consequence postulating large LOCA from SFP.
 JNES plans to conduct a study on LOCA at SFP to accumulate basic data to
establish, for example, success criteria of the fuel cooling procedures
using spray cooling system and others available means.
Steam flow cooling
Air flow cooling
Spray flow cooling
Wspray
Natural
circulatio
n
Tsurf
Pdecay
h
Wloca
• Effectiveness of steam cooling
in the case of small LOCA
depending on the leak flow rate
and fuel assembly distribution.
Wloca
• Multi-dimensional natural
circulation flow behavior
depending on fuel assembly
distribution, etc.
Wloca
• Effectiveness of spray flow
cooling for large LOCA
• Data acquisition for assessment
of models and methods
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3/18/2013
Development of Evaluation Methods
of Safety Culture
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 The National Diet of Japan Fukushima Nuclear Accident Independent
Investigation Commission submitted the report to the Diet on July 5, 2012.
 “Organizational issues …” in its executive summary:
 There were many opportunities for NISA, NSC and TEPCO to take measures that
would have prevented the accident, but they did not do so.
 The Commission found that the actual relationship lacked independence and
transparency, and was far from being a “safety culture.” In fact, it was a
typical example of “regulatory capture,” in which the oversight of the industry
by regulators effectively ceases.
http://warp.da.ndl.go.jp/info:ndljp/pid/3856371/naiic.go.jp/en/
 JNES has started activities for
 OECD/NEA CSNI WGHOF (WG on
fostering internal safety culture
Human and Organizational Factors) has
and developing safety culture
initiated a new task on “Human
evaluation methods for both
intervention and performance under
licensees and regulatory body.
extreme conditions”:
 OECD/NEA has started a task on
 Decision making with limited
decision making under extreme
information and reduced resources
conditions. JNES is participating in it.
under very stressful circumstances.
 Taking measures under extreme
 In such HOF areas, international
environmental conditions and
cooperation is expected to play an
difficult accessibility and operability
important role.
Off-site Radiological Effect on
Residents and Workers
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 JNES is conducting an evaluation of off-site radiation effects due to living and
restoration activities upon request from the Local Nuclear Emergency Response
Headquarters.
 Evaluation of resident exposure in
 Evaluation of exposure due to wild fire
 About 70% area of Fukushima
prefecture is forest.
 Simplified dose evaluation tool
applicable even under insufficient fire
information has been developed and
provided to local firefighter offices.
decontaminated areas
Basic
concept
Basic
concept
Assessment
Method
×
Land use
indicator
Radioactive
material
concentration
×
Terrain
indicator
Protective
Wind
× velocity ×
×
mask
indicator
indicator
Wind
direction
indicator
Exposure dose
=
Dose Evaluation
Summary
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 The Diet Accident Investigation Commission pointed out “Regulatory
Capture” as one of “fundamental causes.” Lack of technical expertise
and competence could have been a contributing factor.
Safety research needs to contribute to strengthening of regulatory
technical bases.
 After Fukushima, relevant acts were amended and implementation of SA
measures becomes a legal requirement. NRA has established the draft
new safety standards. JNES and JAEA/NSRC have initiated various safety
research activities such as:
 External hazard evaluation
 SA progression/source terms, effectiveness of existing and new
SA measures, etc.
 SA measures at SFPs
 HOF issues including safety culture
 Such topics are commonly discussed in many countries as lessons learned
from Fukushima. The international cooperation and sharing
information become more and more important.
 Japan is hosting the OECD/NEA BSAF project, “Benchmark study of
the accident at the Fukushima-Daiichi NPS”, to improve SA codes and
analyze accident progression and current core status in detail.
http://www.oecd-nea.org/jointproj/bsaf.html
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3/18/2013
Appendix
Reform of Nuclear Regulatory Organizations
15
H. Yamagata, NRA, Japan’s Progress to
Enhance Nuclear Safety, OECD/NEA CNRA,
3-4 Dec. 2012, Paris.
Appendix
An Example of Proposed Change:
Aging Management
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Former legislation
 There is not limit for plant life.
 Requirements:
 Regulatory annual
inspection every 13 to 24
months
 Comprehensive aging
management evaluation
before 30 years and every
10 years afterwards
Start of Commercial Operation
Regulatory Inspection (every 13 – 24 months)
Utility’s Periodic Safety Review (PSR) (every 10 years)
Utility’s Evaluation for Long-Term Operation
Re-evaluation Every 10 Years
30 Years
10 Years
10 Years
Proposed legislation
 “Limit of operation” of 40 years will be introduced.
 As an exception, one shot extension of a certain period (<20 years)
will be approved only when compliance with the regulatory standards is
confirmed.
Source: Reform of Japan’s Nuclear Safety Regulation, January, 2012
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